Why won't this girl respond to my Facebook messages?

[Raindomize]

Hello everyone. This is a long post, so read if you wish and if you do, please help me out!

So there's this girl I like and I try to chat her on Facebook, but she won't respond.

Here's the story:
This girl and I go to the same school and we're in the same grade. We finish our finals, and now we're on break.
I get on Facebook and I ask her (through chat) how her break has been and she said that she's doing fine. Then she asks me how I'm doing, which obviously means she expects a reply right? So I respond, telling her that I'm doing fine as well. The funny thing is though, she doesn't see or respond to that message despite obviously asking for an answer. You know the Facebook "seen" feature? Well there's no sign that she's "seen" my response even though she's asked me a question.

So I wait a few days and then ask her a question. There's no sign that she's "seen" that message either! On top of that though, she has been posting stuff and she has been showing signs of recent activity (e.g. liking and commenting on statuses and photos, "checking in" with apps, etc.), so I'm wondering why the heck she hasn't responded, much less "seen" my messages!

I'm tempted to ask her another question, or at least do something to get her attention, but I don't want to be viewed as needy or desperate.

I hear that the Yahoo! community is nice, and hopefully whoever's reading this can give me some nice feedback.

Thank you in advance!
I forgot to mention. I think she has a boyfriend but I'm not sure. It says on Facebook that she's in a relationship with someone, but his name is unfamiliar and:
1. He's not from our school.
2. He's probably living in the U.S.
3. I'm not sure if the girl is all that connected/close to him.
4. On that guy's Facebook page, it doesn't say he's in a relationship with her.

I only heard his name mentioned on one occasion, and that was when a friend of the girl I like mentioned that the girl I like should see her "boyfriend" when he comes here.
I forgot to mention. I think she has a boyfriend but I'm not sure. It says on Facebook that she's in a relationship with someone, but his name is unfamiliar and:
1. He's not from our school.
2. He's probably living in the U.S.
3. I'm not sure if the girl is all that connected/close to him.
4. On that guy's Facebook page, it doesn't say he's in a relationship with her.

I only heard his name mentioned on one occasion, and that was when a friend of the girl I like mentioned that the girl I like should see her "boyfriend" when he comes here.